1. Field of the Invention
The present invention relates to an improvement of a gas-insulated (or insulating gas-filled) disconnecting switch. In particular, the invention concerns an improvement of the disconnecting switch which is effective for preventing a ground fault due to arc-over which may possibly be produced in a circuit opening operation.
2. Description of the Prior Art
Usually, the disconnecting switch is employed in a power transmission system in combination with a circuit breaker. When a power line is to be opened, a main circuit is first opened by means of the circuit breaker and the disconnecting switch is subsequently opened in a substantially dead state (i.e. no-current state). However, there arises recently some applications where the disconnecting switch is to be opened and/or closed in a live state in which a line charge current of the order of several amperes is present. Under the circumstance, it is required that the disconnecting switch has a performance to deal with such operation.
Generally, the gas-insulated disconnecting switch is configured such that a disconnector including a movable electrode and a stationary electrode is mounted in an electrically insulated state within a metallic container which is grounded and filled with a high insulation gas in a hermetically sealed manner. The relative speed of the movable electrode to the stationary electrode for separating the former from the latter (this speed will hereinafter be termed as "separating speed") is relatively low in a range of 0.5 m/s to 1.5 m/s. Further, the disconnecting switch is not imparted with a powerful arc-extinguishing performance. Consequently, when the charge current of a high voltage line is to be broken in the live state by means of the disconnecting switch of the structure mentioned above, arc will be repeatedly produced between the movable electrode and the stationary electrode as the former is being separated from the latter until the distance between both electrodes (hereinafter called as "inter-electrode distance") has attained a sufficient length. Such arc-over will provide no problems so far as the arcing is confined within the space between both electrodes. However, the inventors have found that in the conventional insulating gas-filled disconnecting switch, there arises such case where the arc reaches the grounded metal container from one of the electrodes in the circuit opening operation, resulting in a ground fault and giving rise to serious problems.